The present invention relates to a self-developing type photographic apparatus and, more particularly, to such an apparatus having a spread roller system.
Such photographic self-developing systems have a film packet containing a rectangular film area to be developed and a processing fluid supply. The packet is advanced through a gap of a roller system for spreading the processing fluid over the rectangular area of a film unit.
One of the major more serious problems of such self-developing type systems lies in the distribution of the processing fluid. Typically, the spreading over the entire rectangular film area is not uniform and, particularly, in its border regions. The presence of undeveloped portions, of course, makes the finished picture practically worthless.
To solve this problem, the prior art has proposed placing the processing fluid in pouches between two superposed sheet elements which are secured at their common opposite longitudinal edges by edge-binding brackets. Each bracket has portions which extend inwardly away from the respectively associated longitudinal edge and which lie on the external surfaces of the sheet elements. Thus, the packet has margin portions of a greater thickness than those portions intermediate the longitudinal edges.
During the advancement through the gap of the roller system, a pressure is generated intermediate the sheet elements which must be relieved in their margin portions so that the border regions of the film area can be fully developed.
Thus, circumferentially-extending grooves are provided on opposite ends of a roller which is provided with a deformable outer layer. These grooves provide the aforementioned refief function. However, the width and depth of these grooves are very critical for proper development of the border regions of the film area. The deformable layer is about one-tenth of a millimeter, and the depth of the grooves is typically about one-hundredth of a millimeter. If the depth of a groove is too shallow, longitudinal undeveloped strips are formed; if the depth of the groove is too deep, for example, even one micron oversized, not enough processing fluid will be present to develop the trailing corner regions of the film area. The technical aspects associated with holding the mechanical tolerances of the grooves have proven to be extremely costly and very difficult to reliably achieve and maintain in practice.